The best way to explain this is with an example:

If you search for "disney", and request page 1, you will get:

{ "page":1, "results":[ 20 records ], "total_pages":6, "total_results":117 }

For pages 2 through 6, you get what you'd expect:

{ "page":2, "results":[ 20 records ], "total_pages":6, "total_results":117 }
{ "page":3, "results":[ 20 records ], "total_pages":6, "total_results":117 }
{ "page":4, "results":[ 20 records ], "total_pages":6, "total_results":117 }
{ "page":5, "results":[ 20 records ], "total_pages":6, "total_results":117 }
{ "page":6, "results":[ 17 records ], "total_pages":6, "total_results":117 }

At this point, you have retrieved 117 unique TMDb movie IDs.

However, if you then request page 7, you will get:

{ "page":7, "results":[ 20 records ], "total_pages":9, "total_results":175 }

Two of the movies returned in these 20 records are not in the original 117:

74146: Classic Cartoon Favorites, Vol. 5 - Extreme Sports Fun
74148: Classic Cartoon Favorites, Vol. 6 - Extreme Music Fun

For page 8, you get more:

{ "page":8, "results":[ 20 records ], "total_pages":9, "total_results":175 }

Four of these 20 are new:

51313: Esperando la Navidad
39251: Fluppy Dogs
46235: Little Einsteins - The Legend of the Golden Pyramid
126570: The Chronological Donald Volume Three

For page 9:

{ "page":9, "results":[ 15 records ], "total_pages":9, "total_results":175 }

One of which is new:

38566: Winnie the Pooh - ABC's

If you request page 10, you finally get an empty result set:

{ "page":10, "results":[], "total_pages":9, "total_results":175 }

However, note that all total you have only retrieved 172 records - not 175. And, only 124 of those are actually unique.

I have not examined the actual results returned by the web search, but it appears to show this same behavior.

This will put you on "Page 12 of 12" of 117 results: https://www.themoviedb.org/search?query=disney&movie_page=12

This will put you on "Page 13 of 18" of 175 results: https://www.themoviedb.org/search?query=disney&movie_page=13

Page 19 will finally show "We didn't find any movies."

BTW... if you click "formatting help" on the new discussion form, the top of the modal pop-up is outside the viewport and you can't get rid of it. (A preview would be nice too)